Process for producing alloys containing metal of the iron group



Patented Aug. 6, 1935 v UNITED STATES PROCESS FOR PRODUCING ALLOYS CON- TAINING METAL OF THE IRON GROUP Emil Gustaf Torvald Gustai'sson, Stockholm, Sweden No Drawing.

Serial No. 497,078. 1929 12 Claims.

My present invention relates to a process for producing alloys containing one or more of the metals of the iron group, iron, nickel and cobalt,

as base metal, and difilcultly reducible, carbon binding, readily oxidizable metal or metals as alloying constituent or constituents, such as chrome, tungsten, vanadium, titanium and manganese, especially alloys low in carbon.

The main object of the invention is to provide a process of the type described according to which metal alloys may be produced with a really perfect distribution of the alloying metal in the alloy.

To this end the process according to the invenvention comprises preparing a finely divided mixture of base metal, for instance iron sponge, ore of the alloying metal and thermic reducing agent in a quantity required for the reduction of the ore and the desired content in the product of the reducing agent, for instance silicon or aluminium, transforming said mixture, if desired with the use of a suitable binding agent, into briquettes or other form of pieces, and reducing and melting said briquettes or pieces in a suitable furnace in such a way that the base metal, and the alloying metal reduced out of the ore by the thermic reducing agent, are protected against an oxidizing action of the atmosphere in the furnace, and, if desired, also against carbon binding, for instance, from the electrodes or the like.

The thermic reducing agent may preferably consist of silicon, aluminium, calcium or alloys of one or more of these metals and heavy metal, for instance iron, manganese or chrome. As binding agent any suitable binding material may be used. When an alloy low in carbon is to be produced, for instance chromium alloys with a high content of chrome and carbon below 0.1%, a binding agent as low as possible in carbon should be used, for instance finely divided iron containing hydroxid of iron, water-glass or limewhite. In such case the thermic reducing agent should also be as low in carbon as possible. When producing alloys with an extremely low content of carbon such binding materials are to be preferred which on drying for solidification of the briquettes do not absorb carbon dioxide from the drying gases.

If iron is used as base metal, it may consist of any kind of iron that can be obtained in a finely divided state. Granulated and fine-crushed pig iron may be used, if the alloy is to contain a high percentage of carbon. However, iron sponge is as a rule more suitable, as this product can be produced out of finely divided iron ore, so that it is.

56 directly obtained in a finely divided state or by Application November 20, 1930, In Sweden November 22,

subdivision, for instance crushing, may be transformed into finely divided condition. If alloy low in carbon is to be produced the base metal should contain only a small amount of carbon that can enter into the alloy in the melting, and should 5 therefore be produced in a way adapted thereto. Iron sponge produced in the usual manner by reduction with solid carbonaceous material or with gas will, as a rule, contain about 1% carbon, and is therefore not suitable for the production of allow low in carbon if the degree of reduction in the sponge is high. If, however, the degree of reduction is not kept higher than that in melting the sponge remaining iron oxides in the sponge will be suflicient to consume the remaining carbon in same, such a carbon content is insignificant. In that case such sponge is suitable that is produced by reduction of ore with carbonaceous material, for instance charcoal, peat coal, bituminous coal, semi-coke, anthracite or coke, in a quantity less than that theoretically required for complete reduction of the ore, or in such a way that the sponge produced contains a greater quantity of unreduced oxides than carbon entered into the same is able to reduce, produced for instance, with carbon as reducing agent and through heating by the aid of gas partly consuming the reducing carbon, or with reducing gas whilst withdrawing the sponge before being perfectly reduced.

However, the base metal may also be produced in the briquettes proper by admixing in their preparation, instead oLmetal, finely divided ore containing the metal and exposing the briquettes to a reducing treatment at such a temperature that the base metal is reduced without being melted but that reduction of the ore of the base metal and the alloying metal ore by the thermic reducing agent will not to any mentionable degree take place. If the ore of the base metal is iron ore the reduction should, consequently, be carried out at a temperature not exceeding 1100" or better 1000 to 900 C., at which temperatures the thermic reducing agent will not react with the base metal ore or with the ore of the alloy- 45 ing metal. Thereby the reduction of the base metal ore may take place either by admixing in the briquettes finely divided carbonaceous material and supplying to the briquettes the heat required for the reduction of this ore, or by treating 50 .the briquettes with reducing gas, or by a combination of these ways.

In producing low carbon alloys, for instance so-called rustless or acid resistant or high temperature resistant iron and steel with a com- 5 paratively high content of chrome, or 9 to 25%, a content as low as possible of the thermic reducing agent, for instance silicon, is as a rule desired in the final alloy, because the same will in many cases impart to the product qualities not desirable. Rustless steel should thus generally not contain more than 0.25% silicon. To secure such a low content of the reducing agent in spite of the alloying metal being reduced solely by the aid of such thermic reducing agent, the quantity of thermic reducing agent added in the mixture should be kept lower than the theoretical amount required for complete reduction of the ore of the alloying metal and of metal oxides that may remain in the base metal, for instance when chrome ore is used, thus, in shortness of the amount required for the reduction of the chromium oxide and iron oxides contained. If there is a certain quantity of carbon in the base metal acting as reducing agent for the last mentioned oxides the quantity of the thermic reducing agent should be decreased correspondingly. As a rule a shortness of of .thermic reducing agent is suflicient, but also greater shortnesses, for instance 10 to 20%, may in some cases be suitable. If also a content of the reducing agent, for instance silicon, is desired in the alloy the quantity of the reducing agent in the mixture should be kept correspondingly greater.

To prevent oxidation of the readily .oxidizable alloying metal reduced'by the thermic reducing agent, the reduction and melting of the briquettes should preferably be carried out with the briquettes covered by molten slag of a suitable composition,-for instance containing oxide or oxides of the metal or metals that is or are to be reduced by the thermic'reducing agent. Thereby an openhearth furnace or, better, an electric furnace.

with electrodes operating against the bath in the furnace and capable of being raised and lowered may be used. To prevent absorption of carbon in the product by reduction of metal high in carbon out of the slag, the furnace should thereby be operated with the electrodes out of contact with the slag. However, the slag bath should be kept so deep and the voltage used be so adapted in relation to the power supplied that notwithstanding the main part of the heat is developed through the electric resistance in the slag. The oxidation may. also be prevented by using an induction furnace, or a so-called highfrequency furnace for the reduction and melting of the mixture. To prevent admission of air into the smelting chamber of the furnace and thereby oxidation of readily oxidizable metal, also via the slag, there is preferably kept a reducing or neutral atmosphere in the electric furnace, for instance by introducing a reducing or neutral gas, e. g. hydrogen and/or carbon monoxide. When a development of reducing gas takes place through reduction of remaining oxides in the base metal with carbon present in same such an introduction of gas may be superfluous. The reducing atmosphere may also be attained, for instance, by introducing and smelting a small quantity of oxide ore-carbon-charge in a loose or briquetted state, floating on the slag in the furnace, which charge develops the gas required for preventing admission of air to the bath. Suitably ore of the base metal may be used in this charge. Even if the briquettes are smelted lying on or in the slag bath instead of being covered by same such ore-carbon-charge may be used for obtaining a non-oxidizing atmosphere in the fur- -nace, but in this case the charge should be intro duced into the furnace in such way that it does not during the melting come in contact with the briquettes for producing the alloy.

To form a suitable slag slag-forming materials, such as lime, dolomite, quartz or sand, that may be required depending upon the nature of the gangue in the contained ore and the composition of the reducing agent used, may be admixed in the briquetted mixture and/or added directly into the furnace used. The mixture may be supplied into the furnace at one time, for instance of other alloying elements, for instance nickel or manganese, or deoxidation, if required, is suitably made before the metal is tapped from the furnace, during the tapping, or in another furnace in known manner.

The slag formed in the smelting of the mixture will as a rule contain a rather high percentage of alloying metal, especially if a great shortness of thermic reducing agent has been used in the briquettes. Suitably, this content may be utilized to a great or less degree according to the process set forth in my patent No. 1,901,367, i. e. by separating the slag from the alloy obtained immediately after the termination of the smelting, and supplying to the slag the heat that may be required and thermic reducing. agent, prefer ably of the same kind as has been used in the mixture, in a quantity adapted in such way that a-metal rich in the thermic reducing agent is formed out of the metal oxide or oxides in the slag. The metal thus obtained containing, besides base metal and alloying metal, a considerable percentage of reducing agent, for instance 10 to 15% or more, is after tapping and cooling disintegrated and admixed into the mixture for preparing the furnace charge. In a running of long duration there is obtained according to this process a practically even composition of the furnace charge and a practically complete utilization of the ore of the alloying metal contained in the furnace charge, in spite of a shortness of reducing agent being used in same. In producing, for instance, rustless or acid resistant steel with 10 to 20% chromewith ferrosilicon in shortness as reducing agent, the ferrosilicon is when preparing the mixture partly replaced by ferrochromium-silicon obtained out of the slag formed in the smelting through supplying ferrosilicon in excess to said slag. Hereby the finally tapped slag will contain rather little of the valuable chrome metal.

The process according to the invention involves many advantages as compared with the methods hitherto employed for producing the alloys now in question.- A1; present, for instance, rustless iron or steel, is produced by adding expensive low carbon ferrochrome to an iron bath low in carbon, or by reducing chrome ore with ferrosilicon or aluminium in a slag bath above the iron bath. Thereby the distribution of the chrome in the metal bath will not be even, or else in the latter process the content of silicon in the product will readily be rather high or at least diflicultly controllable and uneven, so that the product will not fill the requirements on same. In the present process, on the contrary, there is attained, in consequence of the base metal and the materials required for forming the alloying metal being present in a finely divided and intimate mixture with the different grains closely fixed to one another, that in the melting an immense number of diminutive metal drops are formed with approximately the same composition as the final product. These drops will then join to a homogeneous metal bath in which the alloying metal is in the best possible way uniformly distributed in the base metal. If in the production a shortness of reducing agent is used in the manner mentioned and the bath in the furnace is not brought into contact with carbon or carbon delivering gas, the product will also contain the lowest possible amount of the reducing agent used, for instance silicon, and have a low carbon content.

In comparison with the methods hitherto proposed for producing alloys of the kind now in question directly out of base metal ore and alloying metal ore in one process in an electric furnace, the process according to the invention involves the advantage that the base metal, for instance iron, forming the main part of the final product, may be produced in the cheapest possible way and, if desired, without using electric energy for the reduction, which energy is in the most places not available at a sufficiently low rate. The heat consumption for melting the base metal and for performing the reduction of the alloying metal by the thermic reducing agent being comparatively low, the process will be economically realizable in electric furnaces even if the power rate is comparatively high.

The invention is not limited to the metals, reducing agents, materials or types of furnaces which have hereinbefore been mentioned by way of example only, but comprises any production of metal alloys of the kind now in question with the use of the process set forth.

W at I claim as new and desire to secure by Letters Patent of the United States of America 1. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of base metal in metallic state and in a quantity corresponding substantially to the amount of said base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, briquetting said mixture, and reducing and melting the briquetted mixture in a furnace under non-oxidizing conditions.

2. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diificultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided homogeneous mixture of base metal in metallic state and in a quantity corresponding substantially to the amount of said base metal desired in the alloy, oxide ore containing the alloying metal and silicon bearing thermic reducing agent, briquetting said mixture, and reducing and melting the briquetted mixture in a furnace under nonoxidizing conditions.

3. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided 'mixture of base metal in metallic state, and in a quantity corresponding to the main part at least of the amount of base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, and reducing and melting the mixture in a furnace under non-oxidizing conditions by means of heat developed by electric current induced in the mixture in said furnace.

4. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided, homogeneous mixture of base metal in metallic state and in a quantity corresponding to the main part at least of the amount of base metal desired in the alloy, oxide ore containing the alloylng metal and thermic reducing agent, the latter in a quantity less than that theoretically required for complete reduction of the alloying metal ore and any metal oxides contained in the base metal, briquetting said mixture, and reducing and melting the briquetted mixture in a furnace under non-oxidizing conditions.

5. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively difiicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of base metal in metallic state containing a small amount of oxides of said base metal and carbon in a quantity less than that required for reduction of said oxides, the quantity of base metal corresponding substantially to the amount of base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, the latter in a quantity less than that theoretically required for complete reduction of the alloying metal ore, briquetting said mix ure, and reducing and melting the briquettcd mixture in a furnace under non-oxidizing conditions.

6. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of base metal in metallic state and in a quantity corresponding to the main part at least of the amount of said base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, briquetting said mixture, and reducing and melting in a furnace the briquetted mixture covered by molten slag so as to attain non-oxidizing conditions.

7. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of base metal in metallic state and in a quantity corresponding to the main part at least of the amount of base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, and reducing and melting the mixture in a high frequency electric furnace under non-oxidizing conditions by means of heat developed by electric current induced in the mixture in said furnace.

8. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly metal, which comprises preparing a finely divided mixture of base metal in metallic state and in a quantity corresponding to the main part at least of the amount of base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, and reducing and melting the mixture in a high frequency electric furnace by means of heat developed by electric current induced in the mixture in said furnace while keeping a non-oxidizing atmosphere in the furnace.

9. A process for producing low carbon alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of base metal in metallic state and in a quantity corresponding substantially to the amount of base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, briquetting said. mixture, and reducing and melting the briquetted mixture in an electric furnace while keeping a reducing atmosphere in the furnace.

10. A process for producing alloys containing a preponderant proportion of metal of the iron group as base metal and comparatively difiicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided, homogeneous mixture of base metal in metallic state and in a quantity corresponding substantially to the amount of said base metal desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, the latter in a quantity less than that theoretically required for complete reduction of the alloying metal ore and any oxides contained in the base metal, re-

ducing and melting said mixture in an electric induction furnace under non-oxidizing conditions, separating alloy and slag formed, adding to said slag rich in oxide of the alloying metal thermic reducing agent in such a quantity as to obtain a metal rich in said reducing agent, and admixing said metal in a finely divided state in preparing a new quantity of mixture for the process.

11. A process for producing alloys containing iron in a preponderant proportion and comparatively diflicultly reducible, readily oxidizable metal as alloying metal, which comprises preparing a finely divided mixture of metallic iron in a quantity corresponding to the main part of the iron desired in the alloy, oxide ore containing the alloying metal and thermic reducing agent, briquetting said mixture, and reducing and melting the briquetted mixture in a furnace under nonoxidizing conditions.

12. A process for producing low carbon ironchromium-alloys containing iron in a preponderant proportion, which comprises preparing a mixture of finely divided iron sponge containing iron in a quantity corresponding substantially to the amount of iron desired in the iron-chromium alloy and carbon in a quantity less than that theoretically required for complete reduction of remaining ironoxides in same, finely divided chromite and finely divided low carbon silicon bearing thermic reducing agent, the latter in a quantity less than that theoretically required for complete reduction of the chromite, briquetting said mixture, and reducing and melting the briquetted mixture in a furnace under non-oxidizing conditions.

EMIL GUSTAF TORVALD GUSTAFSSON. 

